#define _CRT_SECURE_NO_WARNINGS 1
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */

bool _isSymmetric(struct TreeNode* p, struct TreeNode* q)
{
    if (p == NULL && q == NULL)
        return true;

    if (p == NULL || q == NULL)
        return false;

    if (p->val != q->val)
        return false;

    else
        return _isSymmetric(p->left, q->right)
        && _isSymmetric(p->right, q->left);
}
bool isSymmetric(struct TreeNode* root) {
    return _isSymmetric(root, root);
}